Field of the Invention
The present invention relates to a battery-powered security sensor system which detects an object to provide or output a warning signal or an alarm signal.
Description of Related Art
As a security sensor system, there is known an AIR (active infrared ray) sensor and a PIR (passive infrared ray) sensor which detect an object through a detection beam such as an infrared ray. In a battery-powered security sensor system having a battery a voltage of the battery is monitored to detect a low battery state, that is, a reduction in battery voltage. When the low battery state is detected during the monitoring, the low battery state is notified by wireless transmission. The security sensor system may control the transmission of the low battery state notification so as to suppress battery power consumption which is caused by the transmission (JP Laid-open Patent Publication No. 2013-127671).
In general, the security sensor system is managed by a control unit in a centralized manner. Upon a notification signal indicative of the low battery state is received by the control unit, an engineer goes to a location where the security sensor system is installed to replace a battery, for which a low battery state is detected, with a new battery. However, in some cases, an engineer cannot immediately go to the installation location, so that it takes considerable time from detection of the low battery state to battery replacement. If the battery goes dead before battery being replaced, the security sensor system would be stopped.
In the device described in the above JP Laid-open Patent Publication No. 2013-127671, in order to postpone the stopping of the device due to the end of the battery life, transmission of a low battery state notification signal is controlled to suppress battery power consumption, but the security sensor system continues a normal object detection operation. Since the security sensor system considerably consumes the battery by the normal object detection operation, battery voltage is substantially decreased even after detection of a low battery state. As such, the battery replacement may not in time, and thus the security sensor system may be stopped.